Reverted PHP req to >= 5.3.3

Reverted the requirement of PHP 5.3.4 matching Symfony's revert

Author: cboden

composer.json

@@ -4,7 +4,7 @@
     "keywords": ["event-loop"],
     "license": "MIT",
     "require": {
-        "php": ">=5.3.4"
+        "php": ">=5.3.3"
     },
     "suggest": {
         "ext-libevent": ">=0.0.5"